20813281 has 4 divisors (see below), whose sum is σ = 21320964. Its totient is φ = 20305600.

The previous prime is 20813279. The next prime is 20813291. The reversal of 20813281 is 18231802.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 6974881 + 13838400 = 2641^2 + 3720^2 .

It is a cyclic number.

It is not a de Polignac number, because 20813281 - 2¹ = 20813279 is a prime.

It is a super-2 number, since 2×20813281² = 866385331969922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20813201) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 253780 + ... + 253861.

It is an arithmetic number, because the mean of its divisors is an integer number (5330241).

Almost surely, 2^20813281 is an apocalyptic number.

It is an amenable number.

20813281 is a deficient number, since it is larger than the sum of its proper divisors (507683).

20813281 is an equidigital number, since it uses as much as digits as its factorization.

20813281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 507682.

The product of its (nonzero) digits is 768, while the sum is 25.

The square root of 20813281 is about 4562.1574939934. The cubic root of 20813281 is about 275.0722939409.

The spelling of 20813281 in words is "twenty million, eight hundred thirteen thousand, two hundred eighty-one".